Uncertain Actuator Failures Research Articles

Fully distributed practical fixed-time fault-tolerant consensus of nonlinear multiagent systems

In this article, the practical fixed-time fault-tolerant consensus problem of a class of first-order nonlinear multiagent systems with actuator faults is investigated. Owing to the existence of uncertain actuator failures (multiplicative faults and additive faults) and non-linearities, it is challenging to study the fixed-time consensus problem of such multiagent systems in a fully distributed approach. To get over this challenge, a fully distributed adaptive protocol that utilizes adaptive techniques is proposed. Under this control protocol, multiagent systems can achieve consensus, and by adjusting controller parameters, the consensus error can converge to the acceptable bounded region in a fixed time. In addition, due to the introduction of adaptive parameters, the design of the control protocol is not dependent on any global network topology information, which means the control protocol is fully distributed. Therefore, the proposed scheme has better scalability and wider applicability. Finally, the simulation results are proposed to validate the fault-tolerant ability and fully distributed characteristics of the presented scheme.

ADP-based online compensation hierarchical sliding-mode control for partially unknown switched nonlinear systems with actuator failures

This article investigates an adaptive dynamic programming-based online compensation hierarchical sliding-mode control problem for a class of partially unknown switched nonlinear systems with actuator failures and uncertain perturbations under an identifier-critic neural networks architecture. Firstly, by introducing a cost function related to hierarchical sliding-mode surfaces for the nominal system, the original control problem is equivalently converted into an optimal control problem. To obtain this optimal control policy, the Hamilton–Jacobi–Bellman equation is solved through an adaptive dynamic programming method. Compared with conventional adaptive dynamic programming methods, the identifier-critic network architecture not only overcomes the limitation on the unknown internal dynamic but also eliminates the approximation error arising from the actor network. The weights in the critic network are tuned via the gradient descent approach and the experience replay technology, such that the persistence of excitation condition can be relaxed. Then, a compensation term containing hierarchical sliding-mode surfaces is used to offset uncertain actuator failures without the fault detection and isolation unit. Based on the Lyapunov stability theory, all states of the closed-loop nonlinear system are stable in the sense of uniformly ultimately boundedness. Finally, numerical and practical examples are given to demonstrate the effectiveness of our presented online compensation control strategy.

Fuzzy Adaptive Fault Tolerant Time-Varying Formation Control for Nonholonomic Multirobot Systems With Range Constraints

This article studies the fault tolerant tracking problem of time-varying formation for nonholonomic multirobot systems. Uncertain nonlinear dynamics are approximated by employing fuzzy logic systems (FLSs), and based on the adaptive backstepping recursive procedure and dynamic surface technology, a fuzzy adaptive formation tracking control scheme is developed. It is notable for formation to achieve collision avoidance and connectivity maintenance, so the prescribed performance methodology is introduced to solve the constrained range problem of distance and angle. Meanwhile, in order to compensate the effect from the infinite number of uncertain actuator failures, the robots can maintain interacting with their leader at the moment of actuator faults, and also uninterruptedly track the time-varying referenced trajectory from the leader, a novel decentralized adaptive fault tolerant control (AFTC) strategy is further proposed for time-varying formation and guarantees all signals are semi-global uniformly ultimately bounded (SGUUB). Finally, the effectiveness of AFTC strategy is illustrated perfectly for nonholonomic multirobot systems.

A Modified Robust Adaptive Fault Compensation Design for Spacecraft with Guaranteed Transient Performance

A modified, robust adaptive fault compensation design is proposed for rigid spacecraft systems with uncertain actuator failures and unknown disturbances. The feedback linearization method is first introduced to linearize the nonlinear dynamics, and a model-reference adaptive controller is designed to suppress the unknown external disturbances and stabilize the linearized system. Then, a composite adaptive controller is developed by integrating multiple controllers designed for the corresponding actuator failure conditions, which can handle the essentially multiple uncertainties (failure time, values, type, and failure pattern) of actuator failures simultaneously. To further improve the transient performance problem in the failure compensation control, an H∞ compensator is introduced as an additional item in the basic controller to attenuate the adverse effects on tracking performance caused by parameter estimation errors. From the theoretical analysis and simulation results, it is obvious that the designed scheme can not only guarantee the stability of the closed-loop system is stable and asymptotical tracking properties for a given reference signal but also greatly improve the transient performance of the spacecraft system during the process of failure compensation.

Adaptive Fuzzy Actuator Failure Compensation Control for a Class of MIMO Nonlinear Systems

In this paper, an adaptive fuzzy control scheme is developed for a class of uncertain multi-input multi-output (MIMO) nonlinear systems with uncertain actuator failures. Within this scheme, a fixed grouping of redundant actuators and a proportional actuation scheme for each group are considered. Afterward, a fuzzy system is used for the online approximation of a nominal control vector. The parameter adaptation laws for the nominal controller are driven by the prediction error, which is defined as the difference between the unknown nominal controller and the fuzzy controller. The proposed controller can compensate for both total and partial loss of effectiveness failure types. Closed-loop system stability and convergence properties of the tracking errors are proved based on Lyapunov theory. A piecewise analysis is carried out to prove that these properties hold despite the presence of parameter jumps caused by abrupt failures. A simulation study is carried out on a redundant joint two-link robot manipulator with joint failures at each link. Simulation results show the effectiveness of the proposed control scheme.

Adaptive Actuator Fault Compensation and Disturbance Rejection Scheme for Spacecraft

An adaptive actuator failure compensation scheme is proposed for attitude tracking control of spacecraft with unknown disturbances and uncertain actuator failures. A new feature of this adaptive control scheme is the adaptation of the failure pattern parameter estimates, as well as the failure signal parameter estimates, for direct adaptive actuator failure compensation. Based on an adaptive backstepping control design, the estimates of the disturbance parameters are used to solve the disturbance rejection problem. Without the requirement of additional fault detection mechanism, the switching function is designed to automatically locate and turn off the unknown faulty actuators by observing a control performance index. The asymptotic stability of the system output in the presence of actuator failures is rigidly proved through standard Lyapunov approach, while the other signals of the closed-loop system are guaranteed to be bounded. Simulation results verify the desired adaptive actuator failure compensation performance.

Adaptive Actuator Failure Compensation Control Schemes for Uncertain Noncanonical Neural-Network Systems.

In this article, direct adaptive actuator failure compensation control is investigated for a class of noncanonical neural-network nonlinear systems whose relative degrees are implicit and parameters are unknown. Both the state tracking and output tracking control problems are considered, and their adaptive solutions are developed which have specific mechanisms to accommodate both actuator failures and parameter uncertainties to ensure the closed-loop system stability and asymptotic state or output tracking. The adaptive actuator failure compensation control schemes are derived for noncanonical nonlinear systems with neural-network approximation, and are also applicable to general parametrizable noncanonical nonlinear systems with both unknown actuator failures and unknown parameters, solving some key technical issues, in particular, dealing with the system zero dynamics under uncertain actuator failures. The effectiveness of the developed adaptive control schemes is confirmed by simulation results from an application example of speed control of dc motors.

Fuzzy finite-time stable compensation control for a building structural vibration system with actuator failures

This paper investigates finite-time stability vibration control for a building structure system in the presence of actuator failure. The dynamic compensation approach for seismic waves improves the control performance by considering such waves as an unknown nonlinear item in the system. In the control design, this item is approximated via the adaptive fuzzy control method. In addition, it is considered that actuators can fail and therefore lessen, the effectiveness of the suppression of building structure vibration. An adaptive failure compensation method is proposed to address this problem. Moreover, to rapidly suppress vibration, a finite-time active vibration controller is designed in combination with a failure compensation method. Under the proposed control strategy, the building structure system with uncertain actuator failures can be guaranteed to be stable in finite time. Finally, examples of different failure cases are presented to demonstrate the anti-seismic effectiveness of the proposed method.

Adaptive Dynamic Programming-Based Fault-Tolerant Position-Force Control of Constrained Reconfigurable Manipulators

This article presents a novel fault-tolerant position-force optimal control method for constrained reconfigurable manipulators with uncertain actuator failures. On the basis of the radial basis function neural network (RBFNN)-estimated manipulators dynamics, the proposed force-position error fusion function and the estimated actuator failure are utilized to construct an improved optimal performance index function, which reflects the faults and optimizes system comprehensive performance as well as the energy consumption simultaneously. Based on the policy iteration (PI) scheme and the adaptive dynamic programming (ADP) algorithm, the Hamiltonian-Jacobi-Bellman (HJB) equation is solved by constructing the critic neural network (NN), and then the approximated fault-tolerant position-force optimal control policy can be derived correspondingly. The closed-loop manipulator system is proved to be asymptotically stable by using the Lyapunov theory. Finally, simulations are provided to demonstrate the effectiveness of the proposed method.

Extended dimension fuzzy adaptive control for nonlinear uncertain stochastic systems with actuator constraints

In this paper, an extended dimension fuzzy adaptive control for nonlinear uncertain stochastic systems with actuator constraints is investigated. The approximation error is introduced into the control scheme as a time-varying function by extended dimension fuzzy logic systems (FLSs). Besides, the sign function as a norm of the FLSs vector, in order to reduce the amount of calculation, will create a challenging chattering problem. Further, actuator failures usually are uncertain in time, pattern, and value and may also occur in practice. In order to handle the above issues, backstepping technology is applied to stabilize stochastic nonlinear system with stochastic disturbance and uncertain actuator failures. It is proved that the asymptotic convergence performance and predetermined transient tracking error performance are guaranteed to be within a pre-established sound whether the actuator fails or not. Finally, simulation results have demonstrated the proposed theoretical results.

Finite-Time Fault-Tolerant Control for Nonlinear Systems With Input Quantization and Its Application

This brief studies the control problem for nonlinear systems with uncertain actuator failures and input quantization. First, a hysteretic quantizer is applied to reduce chattering in the quantized signals. Then, using the backstepping technique, a finite-time fault-tolerant controller is designed. In addition, the control input is quantized by the hysteretic quantizer. It is proved that the global finite-time stability can be ensured for the nonlinear systems with uncertain actuator failures and quantized input signals. Finally, the simulation example of the hydraulic system is presented to verify the established control method.

Direct adaptive control of a flexible spacecraft with disturbances and uncertain actuator failures

Abstract This paper addresses the design of a new adaptive attitude tracking control strategy for a flexible spacecraft system in the presence of external disturbances and uncertain failures of redundant reaction wheels. The proposed strategy does not depend on the exact model of the spacecraft and can compensate for a more general class of time-varying and state-dependent failures that reaction wheels may undergo in a practical environment. The controller is built around an integrated adaptive approximation based design that accommodates for both system and actuator failure uncertainties. The controller parameter update law is derived to minimise the control prediction error. Unlike most existing actuator failure compensation techniques which are limited to special cases of actuator failures, the proposed controller can compensate for a larger set of actuator failures with time-varying patterns. Closed-loop system stability and tracking performance are proved using Lyapunov stability theory. Parameter jumps caused by abrupt failures are also taken into consideration during the stability proof. A simulation study is performed on a spacecraft with flexible solar array actuated by redundant reaction wheels. The results show the effectiveness and feasibility of the proposed actuator failure compensation controller compared to other controllers from the literature.

Adaptive Compensation of Actuator Failures using Multiple Models

In this paper, a novel actuator failure compensation scheme is proposed for affine nonlinear uncertain systems subject to actuator faults/failures unknown in time, magnitude and pattern. The proposed control methodology utilizes a backstepping procedure integrated with multiple estimation models to estimate failure induced parametric uncertainties and unknown system parameters. Relative to existing direct adaptive backstepping based fault compensation strategies, the proposed fault tolerant control (FTC) method yields a faithful accommodation of uncertain actuator failures while ensuring satisfactory output transient and steady state performances. Further, compared to multiple model based adaptive FTC design, the proposed methodology circumvents the issues of stability due to switching between different models and utilizes a minimum number of estimation models for parameter estimation without sacrificing the output performance and thereby reducing the computational burden. Simulation results illustrate the effectiveness and applicability of the proposed method to FTC design problem for longitudinal pitch control of Boeing 747-100/200 aircraft.

Adaptive actuator failure compensation for multivariable feedback linearizable systems

SummaryA feedback linearization‐based adaptive control scheme is developed for multivariable nonlinear systems with redundant actuators subject to uncertain failures. Such an adaptive controller contains a direct adaptive actuator failure compensator to compensate the uncertain actuator failure, a nonlinear feedback to linearize the nonlinear dynamics, and a linear feedback to stabilize the linearized system. The key new design feature is the estimation of both the failure patterns and the failure values, for direct adaptive actuator failure compensation, newly developed for multivariable feedback linearizable nonlinear systems. With direct control signal adaptation, the adaptive failure compensation design ensures closed‐loop stability and asymptotic output tracking in the presence of actuator failure uncertainties. Simulation results from an application to attitude control of a near‐space vehicle dynamic model are presented to verify the desired system performance with adaptive actuator failure compensation. Copyright © 2015 John Wiley & Sons, Ltd.

An adaptive actuator failure compensation scheme for a cooperative manipulator system

SUMMARYThis paper develops a new adaptive actuator failure compensation algorithm for the control of a cooperative robotic system subject to uncertain actuator failures. The benchmark robotic system has two manipulators to balance a rigid platform, and the right-side manipulator contains one actuator and the left-side manipulator has two actuators (one of which may fail during system operation, but it is uncertain how much, when and which actuator may fail). The developed adaptive actuator failure compensation scheme, based on adaptive integration of three individual failure compensators and direct adaptation of controller parameters, is capable of ensuring desired closed-loop stability and asymptotic output tracking, despite the failure uncertainties. Such an adaptive actuator failure compensation method is extended to control of a general cooperative robotic system. Simulation results are shown to verify the desired adaptive failure compensation control performance.

Adaptive fault-tolerant automatic train operation using RBF neural networks

In order to accommodate actuator failures which are unknown in amplitude and time, adaptive fault-tolerant control schemes are proposed for automatic train operation system. Firstly a basic design scheme on the basis of direct adaptive control is considered. It is demonstrated that, when actuator failures occur, asymptotical speed and position tracking are guaranteed. Then a new user-friendly control scheme is proposed which can eliminate the undesirable chattering phenomenon, which is the defect of the previous method. Simulation results verify the effectiveness of established theoretical results that satisfactory speed tracking and position tracking can be guaranteed in the presence of uncertain actuator failures in automatic train operation systems.

Adaptive actuator failure compensation and disturbance rejection scheme for spacecraft

An adaptive actuator failure compensation scheme is proposed for attitude tracking control of spacecraft with unknown disturbances and uncertain actuator failures. A new feature of this adaptive control scheme is the adaptation of the failure pattern parameter estimates, as well as the failure signal parameter estimates, for direct adaptive actuator failure compensation. Based on an adaptive backstepping control design, the estimates of the disturbance parameters are used to solve the disturbance rejection problem. The unknown disturbances are compensated completely with the stability of the whole closed-loop system. The scheme is not only able to accommodate uncertain actuator failures, but also robust against unknown external disturbances. Simulation results verify the desired adaptive actuator failure compensation performance.

A discrete‐time indirect adaptive multiple‐model actuator failure compensation scheme

SummaryA new discrete‐time actuator failure compensation control scheme is developed, using a multiple‐model adaptive control approach which has the capacity to achieve faster and more accurate compensation of failure uncertainties. An individual adaptive system, for each possible failure pattern in a failure pattern set of interest for compensation, is designed using an indirect model reference adaptive control scheme for actuator failure compensation. A multiple‐model control switching mechanism for discrete‐time systems is set up by finding the minimal performance index to select the most appropriate control law. The performance indices are based on the adaptive estimation errors of individual parameterized systems with actuator failures. Simulation results from an aircraft flight control system example are presented to show the desired closed‐loop system stability and tracking performance despite the presence of uncertain actuator failures. Copyright © 2014 John Wiley & Sons, Ltd.

Adaptive Actuator Failure and Structural Damage Compensation of NASA Generic Transport Model

This paper studies design and evaluation of a multivariable model reference adaptive control (MRAC) scheme for aircraft systems under simultaneous actuator failures and structural damage. A key design condition–system infinite zero structure is investigated for nominal and posthazard aircraft systems and the invariance of this essential condition is concluded under realistic failure and damage conditions. The multivariable model reference adaptive control scheme is developed to ensure stability and asymptotic output tracking for the aircraft in the presence of uncertain actuator failures and structural damage. The developed fault-tolerant control design is evaluated by a high-fidelity nonlinear aircraft model–the NASA generic transport model.

Direct adaptive actuator failure compensation control: a tutorial

A resilient control system is expected to have the capacity to restore the desired system stability and tracking performance in the presence of uncertain system faults such as actuator failures. While redundant actuators are used for actuator failure accommodation, uncertain actuator failures, whose failure time, pattern, and values may be unknown, can bring new challenges to feedback control design as such uncertain failures can introduce large structural, parametric, and actuation uncertainties. Two technical issues are associated with using redundant actuators: how redundant actuators should be coordinated for effective failure compensation control, and how a feedback control law should be adaptively designed to compensate uncertain actuator failures. In this paper, we present a tutorial on direct adaptive failure compensation-based solutions to these issues for different types of control systems: state tracking using state feedback, output tracking using state feedback or output feedback, for linear, non-linear, and multi-input multi-output systems. We give an overview on such adaptive actuator failure compensation designs which have special capacities to effectively use actuation redundancy to handle uncertain actuator failures, using either direct or indirect adaptive control approaches for direct adaptive actuator failure compensation without explicit failure detection, for fast and effective failure accommodation.